As illustrated in FIG. 1, a pneumatically driven blood pump consists of a relatively rigid spherical pump casing 112 which is subdivided by a thin, flexible diagraphm 111 into a blood chamber 113 and an air chamber 114. An inlet flap valve 115 and outlet flap valve 116 are installed in the pump casing on the side of the blood chamber. An air tube 43 connects the air chamber 114 to a chamber 42 within a cylinder 3 in which a slideable piston 1 is mounted. When the piston 1 is moved toward the tube 43, the air pressure is increased in the chamber 114 and exerts a pressure through the diphragm 111 on the blood in the chamber 113, which has been completely filled through the inlet flap 115. If this pressure reaches the opening pressure of the outlet flap 116, the blood flows out through the now completely opened flap 116.
If the piston 1 is now moved downwardly in the figure, the diaphragm moves in the opposite direction and flap 116 closes. The flap 115 then opens and new blood flows into the blood chamber 113 for the next pump's cycle. This cycle is repeated in accordance with the rhythm of the heart beat.
There are a number of inadequacies in the arrangement depicted in FIG. 1, particularly if two such blood pumps are to be used for the ventricles of a human heart. For example, if the piston were to fail, the patient in whose body the blood pumps had been installed would surely die. Yet, it is difficult to make a mechanical, pneumatic pump absolutely reliable and thus some redundance is necessary. It is also necessary in the use of such blood pumps to take into account that the human body is not an ordinary plumbing system and that the blood pressure and blood flow rate must adapt to meet the body's needs. Because of problems of infections and other medical considerations, it is not considered entirely practical to implant sensor devices which could supply signals to a control system for the pump. Thus, some sort of system is required to non-invasively detect the body's circulatory requirements and to control the blood pump accordingly. Such a blood control system must be sensitive not only to the blood pressure within the circulatory system, but it also must be sensitive to the amount of blood volume flow through the heart. To simply increase the heart rate in order to meet some predetermined circulatory pressure may not be sufficient and may, in fact, even cause a condition known as circulus vitiosus, namely a constantly increasing heart rate with a steadily insufficient volume of blood flow through the heart.
Most importantly, particularly for use in powering a human mechanical heart, the system must be lightweight and portable.